CORROSION PRODUCT ANALYSIS OF CORROSION RESISTANT ANCIENT INDIAN IRON

Abstract*The corrosion product formed on an ancient 0499!year old non!corroded iron clamp was studied by X!ray di}raction "XRD# \ Fourier transform infrared spectroscopy "FTIR # and Mossbauer spectroscopy [ The iron possessed a non!uniform grain structure with dispersed second phase particles [ Microscopy indicated that rust present on the surface was composed of an adherent and compact inner layer and a loose outer layer [ Enrichment of P was observed at the metal!scale interface and in the inner rust layer [ XRD indicated that the rust was amorphous in nature [ The FTIR spectrum provided that the major constituents of the scale were a \ g\ dFeOOH and FePO3[1H1O [ Mosbauer studies further indicated that these constituents were present in a very _ne form \ con_rming the results obtained by XRD [ The presence of a magnetic oxide with a lower _eld strength than that of magnetite was also identi_ed [ The process of protective rust formation on the ancient Indian iron has been elucidated based on the results of the study [ Initially \ the corrosion rate of the iron is high due to the presence of the slag particles which results in enhancement of the P content in the surface [ In the presence of P \ the formation of a protective amorphous compact layer of dFeOOH is catalyzed and this confers corrosion resistance [ The conversion of FeOOH to magnetite is also indicated and this would further improve the corrosion resistance [ Another factor aiding corrosion resistance is the formation of iron phosphates which would lower th